208,931 research outputs found
Electron Photodetachment from Aqueous Anions. III. Dynamics of Geminate Pairs Derived from Photoexcitation of Mono- vs. Poly- atomic Anions
Photostimulated electron detachment from aqueous inorganic anions is the
simplest example of solvent-mediated electron transfer. Here we contrast the
behavior of halide anions with that of small polyatomic anions, such as
pseudohalide anions (e.g., HS-) and common polyvalent anions (e.g., SO32-).
Geminate recombination dynamics of hydrated electrons generated by 200 nm
photoexcitation of aqueous anions (I-, Br-, OH-, HS-, CNS-, CO32-, SO32-, and
Fe(CN)64-) have been studied. Prompt quantum yields for the formation of
solvated, thermalized electrons and quantum yields for free electrons were
determined. Pump-probe kinetics for 200 nm photoexcitation were compared with
kinetics obtained at lower photoexcitation energy (225 nm or 242 nm) for the
same anions, where possible. Free diffusion and mean force potential models of
geminate recombination dynamics were used to analyze these kinetics. These
analyses suggest that for polyatomic anions (including all polyvalent anions
studied) the initial electron distribution has a broad component, even at
relatively low photoexcitation energy. There seem to be no well-defined
threshold energy below which the broadening of the distribution does not occur,
as is the case for halide anions. Direct ionization to the conduction band of
water is the most likely photoprocess broadening the electron distribution. Our
study suggests that halide anions are in the class of their own; electron
photodetachment from polyatomic, especially polyvalent, anions follows a
different set of rules.Comment: to be submitted to J. Phys. Chem. A; 28 pages, 5 figs + Supplemen
Electron Photodetachment from Aqueous Anions. I. Quantum Yields for Generation of Hydrated Electron by 193 and 248 nm Laser Photoexcitation of Miscellaneous Inorganic Anions
Time resolved transient absorption spectroscopy has been used to determine
quantum yields for electron photodetachment in 193 nm and (where possible) 248
nm laser excitation of miscellaneous aqueous anions, including
hexacyanoferrate(II), sulfate, sulfite, halide anions (Cl-, Br-, and I-),
pseudohalide anions (OH-, HS-, CNS-), and several common inorganic anions for
which no quantum yields have been reported heretofore: SO3=, NO2-, NO3-, ClO3-
and ClO4-. Molar extinction coefficients for these anions and photoproducts of
electron detachment from these anions at the excitation wavelengths were also
determined. These results are discussed in the context of recent ultrafast
kinetic studies and compared with the previous data obtained by product
analyses. We suggest using electron photodetachment from the aqueous halide and
pseudohalide anions as actinometric standard for time-resolved studies of
aqueous photosystems in the UV.Comment: 41 page, 6 figures; supplement: 3 pages, 12 figures; to be submitted
to J. Phys. Chem.
Characterization of the nucleophilic reactivities of thiocarboxylate, dithiocarbonate and dithiocarbamate anions
The kinetics of the reactions of thiocarboxylate and thiocarbonate anions with benzhydrylium ions have been determined in acetonitrile solution using laser-flash photolytic techniques. The second-order rate constants (k) correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, as required by the correlation log k (20 ◦C) = sN(N + E) (J. Am. Chem. Soc., 2001, 123, 9500–9512), allowing us to calculate the nucleophile-specific parameters N and sN for these anions. With these parameters, a direct comparison of the reactivities of thiocarboxylate, dithiocarbonate and dithiocarbamate anions with other nucleophiles becomes possible
Highly selective and sensitive macrocycle-based dinuclear foldamer for fluorometric and colorimetric sensing of citrate in water.
The selective detection of citrate anions is essential for various biological functions in living systems. A quantitative assessment of citrate is required for the diagnosis of various diseases in the human body; however, it is extremely challenging to develop efficient fluorescence and color-detecting molecular probes for sensing citrate in water. Herein, we report a macrocycle-based dinuclear foldamer (1) assembled with eosin Y (EY) that has been studied for anion binding by fluorescence and colorimetric techniques in water at neutral pH. Results from the fluorescence titrations reveal that the 1·EY ensemble strongly binds citrate anions, showing remarkable selectivity over a wide range of inorganic and carboxylate anions. The addition of citrate anions to the 1·EY adduct led to a large fluorescence enhancement, displaying a detectable color change under both visible and UV light in water up to 2 μmol. The biocompatibility of 1·EY as an intracellular carrier in a biological system was evaluated on primary human foreskin fibroblast (HF) cells, showing an excellent cell viability. The strong binding properties of the ensemble allow it to be used as a highly sensitive, detective probe for biologically relevant citrate anions in various applications
Bis(2,6-dicarboxypyridinium) dichloride acetone monosolvate
The title compound, 2C7H6NO4 +·2Cl-·C3H6O, crystallizes with two 2,6-dicarboxypyridinium cations, two chloride anions and one acetone molecule in the asymmetric unit. The crystal structure is characterized by alternating cations and by Cl- anions, forming zigzag chains running along the a axis
Syntheses, Raman Spectroscopy and Crystal Structures of Alkali Hexa-fluoridorhenates(IV) Revisited
The A2[ReF6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type P\overline{3}m1, adopting the K2[GeF6] structure type. Common to all A2[ReF6] structures are slightly distorted octahedral [ReF6]2− anions with an average Re—F bond length of 1.951 (8) Å. In those salts, symmetry lowering on the local [ReF6]2− anions from Oh (free anion) to D3d (solid-state structure) occur. The distortions of the [ReF6]2− anions, as observed in their Raman spectra, are correlated to the size of the counter-cations
Caribou reactions to provocation by snowmachines in Newfoundland
Caribou in Gros Morne National Park reacted to provocation by snowmachine with significant differences in their response between years. Upon exposure to snowmachines, caribou were displaced 60 to 237 m from their initial locations. Groups with calves allowed the snowmachines to approach more closely before responding (5 to 600 m) than adult-only groups (30 to 1300 m), and their overall flight distances were less. Time spent in locomotion and overall reaction time were greater for animals engaged in the most sedentary activities (eg. standing; mean = 239 s and mean = 262 s, and lying; mean = 166 s and mean = 273 s) than for animals already engaged in more dynamic activities such as walking (mean = 118 s and mean = 133 s), running (mean = 74 s and mean = 63 s) and feeding (mean = 118 s and mean = 133 s). Annual differences in the response of adult-only groups were not due to differences in the sex ratio of these groups, but may be related to annual variation in winter weather conditions
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